The use of a hand operated pointing device for use with a computer and its display has become almost universal. One form of the various types of pointing devices is the conventional (mechanical) mouse, used in conjunction with a cooperating mouse pad. Mechanical mice typically include a rubber-surfaced steel ball that rolls over the mouse pad as the mouse is moved. Interior to the mouse are rollers, or wheels, that contact the ball at its equator and convert its rotation into electrical signals representing orthogonal components of mouse motion. These electrical signals are coupled to a computer, where software responds to the signals to change by a ΔX and a ΔY the displayed position of a pointer in accordance with movement of the mouse.
In addition to mechanical types of pointing devices, such as a conventional mechanical mouse, optical pointing devices have also been developed. In one form of an optical pointing device, rather than using a moving mechanical element like a ball, relative movement between an imaging surface, such as a finger or a desktop, and photo detectors within the optical pointing device, is optically sensed and converted into movement information. Battery operated optical mice are currently available based on Agilent's ADNS-2020 and ADNS-2030 optical image sensors. Other optical mice are available based on Agilent's ADNS-2001 and ADNS-2051, as well as other optical image sensors.
In a typical optical mouse, a light emitting diode (LED) illuminates the surface under the mouse. Under normal circumstances, the mouse body blocks ambient light from reaching the area of the navigation surface visible to the image sensor. However, when the mouse is lifted, ambient light can provide strong amplitude (but out of focus) images to the image sensor. It is desirable for the optical mouse sensor to report no motion in such situations, as the user is either finished with mouse usage (e.g., the mouse is set aside) or is attempting to reposition the screen pointer due to limited space on the navigation surface.
At present, optical mice use out-of-focus indications, low signal amplitude indications, or zero displacement answers from cross-correlation, in order to detect a mouse lifted condition and keep the screen pointer steady. For the out-of-focus technique, the pictures from the image array are typically passed through a high pass filter, and the output of the high pass filter provides an indication of whether the images are in focus or not. If the images are not in focus, it is likely that the surface under the mouse is not at the correct, normal distance, and the mouse may have been lifted by the user. For the low signal amplitude technique, the total amount of signal output by the image sensor, which could be comprised of both light bouncing off the surface from the LED and ambient light, is measured. When the amplitude of the signal out of the image sensor is low, an indication to stop moving the screen pointer is generated. If a sufficient amount of ambient light strikes the image sensor when the mouse is lifted, a low signal amplitude signal will not be generated, and the screen pointer may continue moving. For the third technique (zero displacement answers from cross-correlation), images are captured and correlated in the normal manner to determine how much motion has occurred. When the mouse is lifted, the captured images are typically blurry and appear to be essentially the same to the mouse, so the mouse typically, but not always, reports zero motion in this situation, causing the screen pointer to stop moving.
These prior methods for detecting a mouse lifted condition are not always reliable. In some cases, the screen pointer moves in an unpredictable path, or jitters in place, when it should remain still, which results in an annoyance to the user and an undesirable consumption of power. If the mouse lifted condition is not detected, the mouse may remain in a full power mode, rather than switching to a sleep mode. For a battery-operated mouse, if the mouse is left upside down or is left unused at the end of a desk for a long period of time, a large amount of battery power can be consumed by not detecting this condition and freezing the screen pointer.
In addition, if there is a large amount of ambient light on the area under the mouse that is being imaged, this ambient light can interfere with navigation accuracy during normal use of the mouse.